FAR 61.51 sets out the regulations for logging flight time. It does not specify the type of logbook that a pilot must use—only that it is in a “manner acceptable to the Administrator.” Before we go any further, we’ll state unequivocally: Electronic logbooks are acceptable to the Administrator.
We’ll also quickly digress to point out that the FAA defines “flight time” in Part 1.1, General Definitions as “Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing.” So, if you start up and sit there idling while you fiddle with things and play with the glass panel while the Hobbs runs, you can’t log it as flight time. It also means that you don’t have to limit the flight time you log to the time while the aircraft is not touching the ground.